Nope dumbledore is definately dead, no changing that he died on the tower and he ain't comming back, and snape would have to have a bloody good reason to why he killed dumbledore as he pleaded for his life.
I've heard that rumor about the 'scar' thing but I'd find it pretty difficul to pick a specific word to end a book as big as book 7 is going to be.
😂 you know your borderlining on saying that Dumbledore was suicidal there, he said it was the next great adventure but that doesn't nesicarily mean he wanted to die, it just means he belived that there was at least one final adventure to look forward too and that he was ready to take it when the time came.
Ok that may be the case, but I doubt it, Dumbledore wanted to help Harry as much as he could, some how I don't think having himself killed would of helped all that much and what would be gained for the good side if he was killed, if anything he'd of made sure the magical would was safe before going out with a bang.